In the case where high frequency stability is desired, such as a base station of mobile phones, for example, an OCXO shown in Patent Document 1 is employed as the most of oscillators. The OCXO keeps a constant temperature of an atmosphere where, for example, a crystal resonator as a piezoelectric resonator, which outputs an oscillation frequency, is placed using a heating unit. Therefore, the oscillation frequency is stable.
On the other hand, an output frequency in the oscillation device may change its oscillation frequency by the time due to such as a mass change caused by substances included in the atmosphere accumulating on the piezoelectric resonator. Conventionally, sufficient aging has been given to the piezoelectric resonator before shipping of a product to reduce an aged deterioration of the oscillation frequency in the market.
In the telecommunication industry, the area of space development, or similar field, a further stabilized oscillation frequency is desired. Therefore, in the case where aging is insufficient due to, for example, a limited delivery deadline when aging is performed to the piezoelectric resonator at a supplier side, there is a concern that a fluctuation of the oscillation frequency caused by an aged deterioration becomes a problem. There is also a concern that taking a long time for aging at the supplier side significantly burdens on speedy distribution of the product.